A number of applications require connection or clamping to a cylindrical object, such as a tube, rod or shaft, for example. Examples of such are for clamping to the steering tube, bicycle seat tube, or handlebar of a bicycle.
Bicycles are widely used for transportation and recreation. A typical bicycle includes a rear wheel carried by a frame and a front wheel carried by a fork which, in turn, is rotatably connected to a forward portion of the frame. In particular, a steering tube is connected at its lower end to the fork and extends through a corresponding passageway defined in the forward portion of the frame. An upper portion of the steering tube is connected to a bicycle stem.
The bicycle stem includes a steering tube clamp portion which clamps to the upper end of the steering tube. A body portion extends generally forwardly and incline from the steering tube clamping portion and terminates at a handlebar clamp portion. The incline is generally upward for mountain biking and downward for road biking, as desired by the rider. Of course, the medial portion of the handlebar is connected to the handlebar clamp portion of the stem. The rider is thus able to steer the front wheel by turning the handlebar.
The bicycle stem is important for proper orientation and positioning of the rider relative to the bicycle. In addition, the stem is desirably relatively strong to avoid potentially catastrophic failure, and is also desirably lightweight to reduce the burden on the rider. Mountain or off-road biking can put especially high demands on the strength of the stem. Road bikes may also place high demands in terms of both required strength and being relatively lightweight on the bicycle stem.
The stem also desirably has relatively high torsional stiffness, that is, a resistance to allowing the handlebar to rotate as the rider pushes on one side while lifting on the other. If the torsional stiffness is too low, the rider's energy is more quickly and wastefully depleted in rotating the handlebar.
Bicycle stems can be made of several different materials that are both light in weight and have high strength properties. Recently, and in an effort to use more lightweight materials, bicycle stems and other bicycle components have been manufactured out of composite materials. The clamp used to secure such bicycle components typically includes two cylindrical halves or clamping members which can be urged together by a fastener, such as a bolt, for example, which extends along an axis defined by the cylindrical halves. More particularly, the cylindrical halves each include corresponding arcuate recesses which, when properly aligned, will press against an outer circumferential portion of the steering tube upon tightening of the bolt to thus clamp the bicycle stem to the steering tube. Such stems are shown, for example, in U.S. Pat. Nos. 5,687,616 and 5,842,385.
The outermost ends of the clamps may define contact points which bite into the bicycle components, thus forming dimples in bicycle components. These dimples are especially common in bicycle components made of more flexible materials, such as aluminum. Such deformations of the bicycle component may be undesirable for a number of reasons. For example, the deformations are aesthetically displeasing and can sometimes cause the clamp to seat within the dimples. When a clamp seats within the dimples good contact is not made with the bicycle object to be clamped. In cases where composite materials are used to form bicycle components, scoring of the bicycle component occurs when the clamp end portions dig into the bicycle component. This scoring is generally undesirable. Over time, the scoring may lead to more serious damage, such as cracks, which may eventually lead to catastrophic failure. Such composite bicycle components are often used on high-end road bicycles, for example. Of course, these same shortcomings extend to other similar clamping applications.
U.S. Pat. No. 3,868,193 to Schott discloses a clamp having portions with a smaller cross sectional area so as to improve bending flexibility. Therefore, when the clamp is tightened around the object to be clamped, it gives way, or bends. Therefore, it is the clamp that is deformed instead of the object being clamped. Unfortunately, this deformation of the clamp can also eventually lead to catastrophic failure of the clamp. Further, in cases where the object to be clamped is made of very brittle material, such as a composite material, the force necessary to deform or crack the material is not great and therefore any tightening of the clamp that allows for end portions of the clamp to bite into the object can still cause catastrophic failure of the object.
A bicycle stem including a handlebar clamping portion that tightens against a composite handlebar may cause cosmetic damage or scratching of the composite material if the clamp portions deform slightly during tightening of the fasteners. This may occur, for example, when opposing clamping portions are configured to define one or more pairs of opposing ends in a preclamped state. As the fasteners are secured and the opposing ends are drawn toward each other for the clamped state, the clamp portions may deform slightly and dig or bite into the composite material causing scratches or indentations in the surface.
U.S. Pat. No. 6,176,640 to Gonczi, for example, discloses an approach to overcome the scratching of a composite steering tube upon clamping. This patent discloses forming flats on the otherwise rounded outer surface of the composite steering tube. Accordingly, the opposing ends of a C-shaped clamp will not contact the steering tube at these flats when in the clamped state. Unfortunately, the overall contact area available for clamping is reduced and careful alignment may be required to ensure that the opposing ends are aligned with a flat.